Space Junk No Threat to Station

As the International Space Station’s smaller, two-person, Expedition 22 crew enjoyed its first full day alone in orbit Tuesday, Mission Control monitored a small piece of space junk until tracking updates showed it would not come close enough to require precautions.

At 11:25 a.m. EST, Flight Director Dana Weigel decided not to awaken the crew based on the latest tracking data on the piece of a Russian Cosmos satellite, estimated to be less than four inches in diameter. Mission Control determined the probability of a collision was so low that there was no need to have the crew make a precautionary move into their Soyuz spacecraft, close hatches and be ready to depart the station.

Kazakh authorities give a warm welcome to the Expedition 21 crew members following their return to Earth aboard the Soyuz TMA-15 spacecraft. Pictured, left to right, are Canadian Space Agency astronaut Robert Thirsk, flight engineer; Russian cosmonaut Roman Romanenko, flight engineer; and European Space Agency astronaut Frank De Winne. Credit: ESA/Stephane Corvaja

The debris had been so small that tracking sensors initially had trouble providing reliable information about how close it might come to the station, but best estimates were that the closest approach would be about 1 kilometer away at 1:19 p.m.

Commander Jeff Williams and Flight Engineer Max Suraev were informed of the possible close pass before they went to bed at 2:30 a.m. following the departure of crewmates Frank De Winne, Roman Romanenko and Bob Thirsk who returned to Earth aboard their Soyuz TMA-15 spacecraft northeast of Arkalyk, Kazakhstan at 2:15 a.m. (1:15 p.m. Kazakhstan time). Williams and Suraev were scheduled to enjoy the first of two full days off Tuesday.

The U.S. Space Command routinely tracks space debris in orbit around the Earth, and reports to NASA any possible “conjunctions” or close passes to the space station.

NASA has a set of long-standing guidelines that are used to assess whether the threat of such a close pass is sufficient to warrant evasive action or precautions to ensure the safety of the crew.

These guidelines essentially draw an imaginary box, known as the “pizza box” because of its flat, rectangular shape, around the space station. This box is about half a mile deep by 15 miles across by 15 miles tall (0.75 x 25 x 25 kilometers). When predictions indicate that the debris will pass close enough for concern and the quality of the tracking data is deemed sufficiently accurate, Mission Control centers in Houston and Moscow work together to develop a prudent course of action.

Sometimes these encounters are known well in advance and there is time to move the station slightly, known as a “debris avoidance maneuver” to keep the debris outside of the box. Other times, the tracking data isn’t precise enough to warrant such a maneuver or the close pass isn’t identified in time to make the maneuver. In those cases, the control centers may agree that the best course of action is to move the crew into the Soyuz spacecraft that are used to transport crew members to and from the station so that they could isolate those spaceships from the station by closing hatches, and then leave the station if the debris were to collide with the station and cause a loss of pressure in the life-supporting module. The Soyuz act as lifeboats for crew members in the event of an emergency.

Mission Control also has the option of taking additional precautions, such as closing hatches between some of the station’s modules, if the likelihood of a collision is great enough.

If the tracking data indicates any extra precautions are needed updates will be provided on the web and NASA TV as appropriate.

Meanwhile, De Winne, Romanenko and Thirsk were met by the Russian Search and Recovery Forces in all-terrain vehicles and were extracted quickly from the upright Soyuz. Russian helicopters normally used for recovery operations were grounded due to low clouds and freezing temperatures.

After being extracted from the Soyuz, the crew was then driven back to Arkalyk to spend the night. On Wednesday (Tuesday night, U.S. time), the crew will helicopter from Arkalyk to Kustanai, and then fly on the Gagarin Cosmonaut Training Center plane to Chkalovsky Airfield near their training base in Star City, Russia, outside Moscow for reunions with their families and dignitaries and the start of a rehabilitation period. Flight surgeons report that the crew is in excellent shape.